The repetitive histone genes of the sea urchins L. pictus and S. purpuratus have been cloned and partially mapped. The proposed experiments will sequence and compare the genes and intervening spacer DNA and precisely locate the 5' and 3' ends of mRNAs on the gene maps. Developmentally regulated histone gene varients will be cloned by recombinant DNA technology and similarly analyzed. Evolutionary intermediates between deuterostomes and protostomes will be analyzed for histone gene organization by restriction enzyme mapping and DNA-DNA hybridization.